Although an impressive number of studies support a central role for amyloid beta-protein (A beta) in the pathogenesis of Alzheimer's disease (AD), in the vast majority of cases, the underlying causes for the peptide's accumulation are unknown. Overproduction of A beta has been implicated in only a few cases (<5%), and newly generated AB is rapidly cleared from the brain, suggesting that A beta-degrading proteases could play a vital role in regulating cerebral levels of the peptide. Although much work has focused on the generation of A beta, relatively little is known about A beta proteolysis, which could be equally or even more important in the pathogenesis and/or potential treatments of AD. The two best-studied A beta-degrading proteases are neprilysin (NEP) and insulin-degrading enzyme (IDE). There is human genetic evidence showing linkage of the IDE region of chromosome 10q to both AD and type 2 diabetes mellitus (DM2) in some populations, which is intriguing in light of the growing evidence that DM2 and hyperinsulinemia are associated with an increased risk of developing AD. The central hypothesis of this proposal is that IDE and NEP are important regulators of A beta levels in vivo and defects in these proteases may underlie some cases of AD. My Aims are to: 1) Determine whether dysfunction of IDE leads to decreased A beta and insulin catabolism in vivo using two animal models, 2) Assess the relative roles in vivo of IDE and NEP in the metabolism of the human isoform of A beta by breeding gene-deleted mice to human APP transgenic mice, 3) Determine the biological significance of the known polymorphisms in the 5' un-translated region (UTR) of the IDE gene in AD families with allelic association to this region of chromosome 10q by quantifying transcripts and using reporter constructs and 4) Examine several aspects of the normal cell biology of IDE, such as a possible GPI-anchor, isoforms in the CSF and serum, and search for natural binding partners. The goal of this K08 proposal is to obtain the necessary scientific training in cell and molecular biology, animal breeding strategies, and statistical analysis to allow the candidate to test the above hypothesis as outlined, and in doing so, allow the candidate to develop into a successful and independent physician-scientist with the skills to help individuals with neurodegenerative dementias. The candidate's career development plan, world-class training environment, and commitment from his Department will allow the realization of this goal.